for Repetition Structures 09/27/04 CS150 Introduction to Computer Science 1

CS150 Introduction to Computer Science 1 Last Time We Counter and sentinel-controlled repetitions Type casting Formatting output Top-down, stepwise refinement Today we will Examine different ways of writing assignments Learn about the increment and decrement operators Start looking at the for repetition structure 09/27/04 CS150 Introduction to Computer Science 1

CS150 Introduction to Computer Science 1 Assignment Operators C++ provides the ability to abbreviate an assignment operator in which the same variable appears on either side of the operator sum = sum + num; Can be abbreviated to sum += num; 09/27/04 CS150 Introduction to Computer Science 1

CS150 Introduction to Computer Science 1 Assignment Operators This abbreviation can be done to the following operators + - * / % Examples, where c = 3, e = 4 c += 7 e %= 2 c *= 3 e /= 4 e -= 1 09/27/04 CS150 Introduction to Computer Science 1

Increment and Decrement Operators ++ is the unary increment operator x++; is the same as x = x + 1; -- is the unary decrement operator x--; is the same as x = x - 1; 09/27/04 CS150 Introduction to Computer Science 1

Pre-increment vs. post-increment Pre Post k = --x; k =x--; k = ++x; k = x++; Increment/ Assign value of x to decrement x k, then increment then assign or decrement x value of x to k 09/27/04 CS150 Introduction to Computer Science 1

CS150 Introduction to Computer Science 1 Example What is the output if i = 2? cout << “Value of x is” << i; cout << “Value of i++ is” << i++; cout << “Value of ++i is” << ++i; cout << “Value of --i is” << --i; cout << “Value of i-- is” << i--; 09/27/04 CS150 Introduction to Computer Science 1

CS150 Introduction to Computer Science 1 Operator Precedence () L->R Parentheses ++, --, static_cast<type>() L->R Unary ++, --, !, +, - R->L Negation, Unary *,/,% L->R Mult, div, mod +, - L->R Add, Subtract <<, >> L->R Insertion/extraction <, <=, >, >= L->R Relational ==, != L->R Equality && L->R And || L->R Or ?: R->L Conditional =, +=, -=, *=, /=, %= R->L Assignment 09/27/04 CS150 Introduction to Computer Science 1

CS150 Introduction to Computer Science 1 For loops 3 main things for loops: Initialization of lcv, testing of lcv, updating lcv For loops provide a concise way to do this for (count = 0; count < 5; count++) cout << count << endl; 09/27/04 CS150 Introduction to Computer Science 1

CS150 Introduction to Computer Science 1 General Format for (initialization expression; loop repetition condition; update expression) { statements; } 09/27/04 CS150 Introduction to Computer Science 1

CS150 Introduction to Computer Science 1 Examples Write a for loop that outputs odd numbers less than 10 Write a program that computes the factorial of a number 09/27/04 CS150 Introduction to Computer Science 1

Localized Declarations for (int i = 0; i < n; i++) cout << i << endl; i is declared ONLY in the loop 09/27/04 CS150 Introduction to Computer Science 1

Rewrite using a while loop for (i = 5; i < 10; i+= 2) cout << i; What does this output? 09/27/04 CS150 Introduction to Computer Science 1

CS150 Introduction to Computer Science 1 Problem Write a program that will print the sum of the odd integers between 1 and 50 inclusive. Write one program using a while and the other using a for loop. 09/27/04 CS150 Introduction to Computer Science 1

CS150 Introduction to Computer Science 1 Problem Write a program that allows the user to enter an unknown number of integer values one at a time. When the user enters -999, you are to terminate the loop and print the following: The sum of all integers inputted The average of all integers inputted The largest integer of all integers inputted 09/27/04 CS150 Introduction to Computer Science 1

CS150 Introduction to Computer Science 1 Summary In today’s lecture we covered Abbreviating assignment operators Increment and decrement operators for repetition structures Readings P. 98 Assignment operators P. 99 - 102 Increment and decrement operators P. 104 - 113 for repetition structures 09/27/04 CS150 Introduction to Computer Science 1